1. Field of the Invention
The invention relates to turbocharged engines, and more particularly to the control of an air bypass valve in a turbocharged engine.
2. Background of the Invention
In general, air bypass valves are known in the art. Air bypass valves are typically operated to prevent compressor surge during various throttle changes. For example, U.S. Pat. No. 7,010,914 to Roberts et al. employs an air bypass valve to prevent a compressor surge on turbocharged engines. Roberts selectively opens a pressure control valve to discharge intake air to reduce compressor outlet pressure and prevent such a surge without changing the throttle position. Roberts is directed to maintaining a shaft speed of turbocharger during enriched operation, such as cleaning NOx traps.
U.S. Pat. No. 6,851,256 to Chamoto et al. discloses the use of variable geometry vanes to cool engine exhaust in a turbocharged engine. In addition, Chamoto controls a bypass passage to control the amount of exhaust gas flowing to the turbine. The bypass passage leads exhaust gas from upstream of the turbine to skip the turbine to control the amount of exhaust gas entering the turbine. When the exhaust gas temperature is greater than a predetermined temperature the control valve closes and more exhaust gas flows to the turbine. Chamoto, however, requires additional expense and complexity to cool the exhaust gas.
There is a need for an efficient and effective exhaust gas cooling system that responds quickly to temperature fluctuations and mitigates problems associated with related art systems.